Castle of Dr. Brain looks like a first person view. This was side-scrolling. I also don't think it was DOS, because...we played it on a mac ^^;
The game probably came out some time around 1994 or 1995...so it probably is either sold or protected, I pretty much just wanna know the name at this point
EDIT: Ok, I guess I need more detail, but the only other thing I've remembered are two rooms; one was a staircase from one floor to the other (there were three floors), that had rainbow colors and made sounds. The only other thing wasn't really a puzzle, it was a minigame where the character had a fish in a thought bubble and you have to catch that type from a pond with the mouse. And when you reach the end (the roof of the castle), there was something like it tells you to start over, and you get a prize for each time (VERY similar to the Treasure _______ games of the super solvers' series), and it may have been based on your percentage completion.
Sorry for the wall of text, I've just been hoping to figure this out ^^;;